Stabilization of CO2 Capture Performance Using Natural Modified CaO-Based Pellets Prepared by Extrusion Granulation

Abstract

CaO-based materials have a high commercialization potential to be used as Calcium-Looping (CaL) sorbents for CO2 capture, owing to their high CO2 sorption capacity and the lowcost raw materials.

The present work focuses on the comparative study of two natural CaO-based sorbents (limestone and wastes of marble powder) with and without alumina incorporation, tested under CaL conditions for CO2 capture. The incorporation of alumina in CaO-based pellets was performed by extrusion followed by calcination at 800 ºC and granulation, using different CaO/Al2O3 ratios (50/50, 60/40 and 70/30) and MethocellTM as pore forming agent. The experiments were carried out in a laboratory scale fixed bed reactor unit along 10 carbonation-calcination cycles using a gas mixture with a CO2 concentration of 25% to mimic the real flue gases in the cement industry, and the calcination was performed under industrial realistic conditions (80% of CO2; 930 ºC) foreseen for the subsequent CO2 utilization.

During the CaL tests a fraction of CaO was converted to calcium aluminate due to its exposure to the process high temperatures. Anyway, the use of modified natural CaO-based pellets containing Al2O3 as structural agent is attractive, since higher CaO conversion values were achieved. The enhanced performance of pellets can be justified by the higher specific surface area and stabilization of CaO crystallite sizes along the cycles promoted by the formation of calcium aluminates. The highest CaO conversion was achieved for the case of 60/40 CaO/Al2O3 pellets, allowing the reduction of the CaO make-up frequency along the time as well as the associated costs.